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Unix (officially trademarked as UNIX®) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson (computer programmer), Dennis Ritchie and Douglas McIlroy. Today's Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations.

As of 2007, the owner of the trademark UNIX® is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX®" (others are called "Unix system-like" or "Unix-like").

During the late 1970s and early 1980s, Unix's influence in academic circles led to large-scale adoption of Unix (particularly of the Berkeley Software Distribution variant, originating from the University of California, Berkeley) by commercial startups, the most notable of which is Sun Microsystems. Today, in addition to certified Unix systems, Unix-like operating systems such as Linux and Berkeley Software Distribution derivatives are commonly encountered.

Sometimes, "traditional Unix" may be used to describe a Unix or an operating system that has the characteristics of either Version 7 Unix or UNIX System V.

Overview Unix operating systems are widely used in both Server (computing)s and workstations. The Unix environment and the client-server program model were essential elements in the development of the Internet and the reshaping of computing as centered in Computer networking rather than in individual computers.

Both Unix and the C (programming language) were developed by AT&T and distributed to government and academic institutions, causing both to be ported to a wider variety of machine families than any other operating system. As a result, Unix became synonymous with "Open system (computing)".

Unix was designed to be porting, computer multitasking and multi-user in a time-sharing configuration. Unix systems are characterized by various concepts: the use of plain text for storing data; a hierarchical file system; treating devices and certain types of inter-process communication (IPC) as files; and the use of a large number of small programs that can be strung together through a command line interpreter using pipeline (Unix)s, as opposed to using a single monolithic program that includes all of the same functionality. These concepts are known as the Unix philosophy.

Under Unix, the "operating system" consists of many of these utilities along with the master control program, the Kernel (computer science). The kernel provides services to start and stop programs, handle the file system and other common "low level" tasks that most programs share, and, perhaps most importantly, schedules access to hardware to avoid conflicts if two programs try to access the same resource or device simultaneously. To mediate such access, the kernel was given special rights on the system, leading to the division between user-space and kernel-space.

The microkernel tried to reverse the growing size of kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a "normal" computer consisted of a hard disk for storage and a data terminal for input and output (I/O), the Unix file model worked quite well as most I/O was "linear". However, modern systems include networking and other new devices. Describing a graphical user interface driven by mouse control in an "event driven" fashion didn't work well under the old model. Work on systems supporting these new devices in the 1980s led to facilities for non-blocking I/O, forms of inter-process communications other than just pipes, as well as moving functionality such as network protocols out of the kernel.

History

In the 1960s, the Massachusetts Institute of Technology, AT&T Bell Labs, and General Electric worked on an experimental operating system called Multics (Multiplexed Information and Computing Service), which was designed to run on the GE-600 series mainframe computer. The aim was the creation of a commercial product, although this was never a great success. Multics was an interactive operating system with many novel capabilities, including enhanced security. The project did develop production releases, but initially these releases performed poorly.

AT&T Bell Labs pulled out and deployed its resources elsewhere. One of the developers on the Bell Labs team, Ken Thompson (programmer), continued to develop for the GE-645 mainframe, and wrote a game for that computer called Space Travel. However, he found that the game was too slow on the GE machine and was expensive, costing $75 per execution in scarce computing time.http://www.bell-labs.com/history/unix/pdp7.html

Thompson thus re-wrote the game in assembly language for Digital Equipment Corporation's PDP-7 with help from Dennis Ritchie. This experience, combined with his work on the Multics project, led Thompson to start a new operating system for the PDP-7. Thompson and Ritchie led a team of developers, including Rudd Canaday, at Bell Labs developing a file system as well as the new multi-tasking operating system itself. They included a command line interpreter and some small utility programs.http://www.bell-labs.com/history/unix/takeshape.html

editor. The dollar-sign at the top of the screen is the prompt printed by the shell. 'ed' is typed to start the editor, which takes over from that point on the screen downwards.

1970s In the 1970s the project was named Unics, and eventually could support two simultaneous users. Brian Kernighan invented this name as a contrast to Multics; the spelling was later changed to Unix.

Up until this point there had been no financial support from Bell Labs. When the Computer Science Research Group wanted to use Unix on a much larger machine than the PDP-7, Thompson and Ritchie managed to trade the promise of adding text processing capabilities to Unix for a PDP-11/20 machine. This led to some financial support from Bell. For the first time in 1970, the Unix operating system was officially named and ran on the PDP-11/20. It added a text formatting program called roff and a text editor. All three were written in PDP-11/20 assembly language. Bell Labs used this initial "text processing system", made up of Unix, roff, and the editor, for text processing of patent applications. Roff soon evolved into troff, the first electronic publishing program with a full typesetting capability. The UNIX Programmer's Manual was published on November 3 1971.

In 1973, Unix was rewritten in the C (programming language), contrary to the general notion at the time "that something as complex as an operating system, which must deal with time-critical events, had to be written exclusively in assembly language".Stallings, William. "Operating Systems: Internals and Design Principles" 5th ed, page 91. Pearson Education, Inc. 2005. The migration from Assembly Language to the High-level programming language C resulted in much more Software quality#Portability software, requiring only a relatively small amount of machine-dependent code to be replaced when porting Unix to other Platform (computing).

AT&T made Unix available to universities and commercial firms, as well as the United States government under licenses. The licenses included all source code including the machine-dependent parts of the kernel, which were written in PDP-11 assembly code. Copies of the annotated Unix kernel sources circulated widely in the late 1970s in the form of a much-copied book by John Lions of the University of New South Wales, the Lions' Commentary on UNIX 6th Edition, with Source Code, which led to considerable use of Unix as an educational example.

Versions of the Unix system were determined by editions of its user manuals, so that (for example) "Fifth Edition UNIX" and "UNIX Version 5" have both been used to designate the same thing. Development expanded, with Versions 4, 5, and Version 6 Unix being released by 1975. These versions added the concept of pipes, leading to the development of a more modular code-base, increasing development speed still further. Version 5 and especially Version 6 led to a plethora of different Unix versions both inside and outside Bell Labs, including PWB/UNIX, INTERACTIVE Systems Corporation (the first commercial Unix), and the University of Wollongong's port to the Interdata 7/32 (the first non-PDP Unix).

In 1978, UNIX/32V, for the VAX system, was released. By this time, over 600 machines were running Unix in some form. Version 7 Unix, the last version of Research Unix to be released widely, was released in 1979. Versions Version 8 Unix, Version 9 Unix and Version 10 Unix were developed through the 1980s but were only released to a few universities, though they did generate papers describing the new work. This research led to the development of Plan 9 from Bell Labs, a new portable distributed system.

1980s graphical user interface. Shown are a number of client applications common to the MIT X Consortium's distribution, including Tom's Window Manager, an Xterm, Xbiff, xload, and a graphical Man page browser.

AT&T licensed UNIX System III, based largely on Version 7, for commercial use, the first version launching in 1982. This also included support for the VAX. AT&T continued to issue licenses for older Unix versions. To end the confusion between all its differing internal versions, AT&T combined them into UNIX System V Release 1. This introduced a few features such as the vi editor and curses (programming library) from the Berkeley Software Distribution of Unix developed at the University of California, Berkeley. This also included support for the Western Electric 3B series of machines.

Since the newer commercial UNIX licensing terms were not as favorable for academic use as the older versions of Unix, the Berkeley researchers continued to develop BSD Unix as an alternative to UNIX System III and V, originally on the PDP-11 architecture (the 2.xBSD releases, ending with 2.11BSD) and later for the VAX-11 (the 4.x BSD releases). Many contributions to Unix first appeared on BSD systems, notably the C shell with job control (modelled on Incompatible Time Sharing). Perhaps the most important aspect of the BSD development effort was the addition of TCP/IP Computer network code to the mainstream Unix Kernel (computer science). The BSD effort produced several significant releases that contained network code: 4.1cBSD, 4.2BSD, 4.3BSD, 4.3BSD-Tahoe ("Tahoe" being the nickname of the Computer Consoles Inc. Power 6/32 architecture that was the first non-DEC release of the BSD kernel), Net/1, 4.3BSD-Reno (to match the "Tahoe" naming, and that the release was something of a gamble), Net/2, 4.4BSD, and 4.4BSD-lite. The network code found in these releases is the ancestor of much TCP/IP network code in use today, including code that was later released in AT&T System V UNIX and early versions of Microsoft Windows. The accompanying Berkeley Sockets Application programming interface is a de facto standard for networking APIs and has been copied on many platforms.

Other companies began to offer commercial versions of the UNIX System for their own mini-computers and workstations. Most of these new Unix flavors were developed from the System V base under a license from AT&T; however, others were based on BSD instead. One of the leading developers of BSD, Bill Joy, went on to co-found Sun Microsystems in 1982 and create SunOS (now Solaris Operating System) for their workstation computers. In 1980, Microsoft announced its first Unix for 16-bit microcomputers called Xenix, which the Santa Cruz Operation (SCO) ported to the Intel 8086 processor in 1983, and eventually branched Xenix into SCO UNIX in 1989.

For a few years during this period (before PC compatible computers with MS-DOS became dominant), industry observers expected that UNIX, with its portability and rich capabilities, was likely to become the industry standard operating system for microcomputers. In 1984 several companies established the X/Open consortium with the goal of creating an open system specification based on UNIX. Despite early progress, the standardization effort collapsed into the "Unix wars," with various companies forming rival standardization groups. The most successful Unix-related standard turned out to be the IEEE's POSIX specification, designed as a compromise application programming interface readily implemented on both BSD and System V platforms, published in 1988 and soon mandated by the United States government for many of its own systems.

AT&T added various features into UNIX System V, such as file locking, system administration, standard streams, new forms of IPC, the Remote File System and Transport Layer Interface. AT&T cooperated with Sun Microsystems and between 1987 and 1989 merged features from Xenix, BSD, SunOS, and System V into System V Release 4 (SVR4), independently of X/Open. This new release consolidated all the previous features into one package, and heralded the end of competing versions. It also increased licensing fees.

During this time a number of vendors including Digital Equipment, Sun, Addamax and others began building Trusted operating system of UNIX for high security applications, mostly designed for military and law enforcement applications.

or CDE, a graphical desktop for Unix co-developed in the 1990s by HP, IBM, and Sun as part of the COSE initiative.

1990s In 1990, the Open Software Foundation released OSF/1, their standard Unix implementation, based on Mach kernel and BSD. The Foundation was started in 1988 and was funded by several Unix-related companies that wished to counteract the collaboration of AT&T and Sun on SVR4. Subsequently, AT&T and another group of licensees formed the group "UNIX International" in order to counteract OSF. This escalation of conflict between competing vendors gave rise again to the phrase "Unix wars".

In 1991, a group of BSD developers (Donn Seeley, Mike Karels, Bill Jolitz, and Trent Hein) left the University of California to found Berkeley Software Design, Inc (Berkeley Software Design). BSDI produced a fully functional commercial version of BSD Unix for the inexpensive and ubiquitous Intel platform, which started a wave of interest in the use of inexpensive hardware for production computing. Shortly after it was founded, Bill Jolitz left BSDI to pursue distribution of 386BSD, the free software ancestor of FreeBSD, OpenBSD, and NetBSD.

By 1993 most commercial vendors had changed their variants of Unix to be based on System V with many BSD features added on top. The creation of the Common Open Software Environment initiative that year by the major players in Unix marked the end of the most notorious phase of the Unix wars, and was followed by the merger of UI and OSF in 1994. The new combined entity, which retained the OSF name, stopped work on OSF/1 that year. By that time the only vendor using it was Digital Equipment Corporation, which continued its own development, rebranding their product Digital UNIX in early 1995.

Shortly after UNIX System V Release 4 was produced, AT&T sold all its rights to UNIX® to Novell. (Dennis Ritchie likened this to the Biblical story of Esau selling his birthright for the proverbial "mess of pottage".http://groups.google.com/group/comp.unix.questions/browse_frm/thread/2f0b5e719fa3a3ec/3fa5e5fe4d58f96b) Novell developed its own version, UnixWare, merging its NetWare with UNIX System V Release 4. Novell tried to use this to battle against Windows NT, but their core markets suffered considerably.

In 1993, Novell decided to transfer the UNIX® trademark and certification rights to the X/Open Consortium.http://groups.google.com/group/comp.std.unix/msg/c9974cf0022884f8 In 1996, X/Open merged with Open Software Foundation, creating the Open Group. Various standards by the Open Group now define what is and what is not a "UNIX" operating system, notably the post-1998 Single UNIX Specification.

In 1995, the business of administering and supporting the existing UNIX licenses, plus rights to further develop the System V code base, were sold by Novell to the Santa Cruz Operation. Whether Novell also sold the copyrights is currently the subject of litigation (see below).

In 1997, Apple Computer sought out a new foundation for its Macintosh operating system and chose NEXTSTEP, an operating system developed by NeXT. The core operating system was renamed Darwin (operating system) after Apple acquired it. It was based on the BSD family and the Mach kernel. The deployment of Darwin BSD Unix in Mac OS X makes it, according to a statement made by an Apple employee at a USENIX conference, the most widely used Unix-based system in the desktop computer market.

2000 to present )

In 2000, SCO sold its entire UNIX business and assets to Caldera Systems, which later on changed its name to The SCO Group. This new player then started legal action against various users and vendors of Linux. SCO have alleged that Linux contains copyrighted Unix code now owned by The SCO Group. Other allegations include trade-secret violations by IBM, or contract violations by former Santa Cruz customers who have since converted to Linux. However, Novell disputed the SCO group's claim to hold copyright on the UNIX source base. According to Novell, SCO (and hence the SCO Group) are effectively franchise operators for Novell, which also retained the core copyrights, veto rights over future licensing activities of SCO, and 95% of the licensing revenue. The SCO Group disagreed with this, and the dispute resulted in the SCO v. Novell lawsuit.

In 2005, Sun Microsystems released the bulk of its Solaris system code (based on UNIX System V Release 4) into an open source project called OpenSolaris. New Sun OS technologies such as the ZFS file system are now first released as open source code via the OpenSolaris project; as of 2006 it has spawned several non-Sun distributions such as SchilliX, Belenix, Nexenta and MarTux.

The Dot-com crash has led to significant consolidation of Unix projects. Of the many commercial flavors of Unix that were born in the 1980s, only Solaris Operating System, HP-UX, and AIX operating system are still doing relatively well in the market, though SGI's IRIX persisted for quite some time. Of these, Solaris has the most market share, and may be gaining popularity due to its feature set and also since it now has an Open Source version.

Standards Beginning in the late 1980s, an open operating system standardization effort now known as POSIX provided a common baseline for all operating systems; IEEE based POSIX around the common structure of the major competing variants of the Unix system, publishing the first POSIX standard in 1988. In the early 1990s a separate but very similar effort was started by an industry consortium, the Common Open Software Environment (COSE) initiative, which eventually became the Single UNIX Specification administered by The Open Group). Starting in 1998 the Open Group and IEEE started the Austin Group, to provide a common definition of POSIX and the Single UNIX Specification.

In an effort towards compatibility, in 1999 several Unix system vendors agreed on SVR4's Executable and Linkable Format (ELF) as the standard for binary and object code files. The common format allows substantial binary compatibility among Unix systems operating on the same CPU architecture.

The Filesystem Hierarchy Standard was created to provide a reference directory layout for Unix-like operating systems, particularly Linux. This type of standard however is controversial, and even within the Linux community its adoption is far from universal.

Components The Unix system is composed of several components that are normally packaged together. By including — in addition to the Kernel (computer science) of an operating system — the development environment, libraries, documents, and the portable, modifiable source-code for all of these components, Unix was a self-contained software system. This was one of the key reasons it emerged as an important teaching and learning tool and has had such a broad influence.

The inclusion of these components did not make the system large — the original V7 UNIX distribution, consisting of copies of all of the compiled binaries plus all of the source code and documentation occupied less than 10Mb, and arrived on a single 9-track magtape. The printed documentation, typeset from the on-line sources, was contained in two volumes.

The names and filesystem locations of the Unix components has changed substantially across the history of the system. Nonetheless, the V7 implementation is considered by many to have the canonical early structure:



Impact The Unix system had significant impact on other operating systems.

It was written in high level language as opposed to assembly language (which had been thought necessary for systems implementation on early computers). Although this followed the lead of Multics and Burroughs large systems, it was Unix that popularized the idea.

Unix had a drastically simplified file model compared to many contemporary operating systems, treating all kinds of files as simple byte arrays. The file system hierarchy contained machine services and devices (such as computer printers, computer terminals, or disk drives), providing a uniform interface, but at the expense of occasionally requiring additional mechanisms such as ioctl and mode flags to access features of the hardware that did not fit the simple "stream of bytes" model. The Plan 9 from Bell Labs operating system pushed this model even further and eliminated the need for additional mechanisms.

Unix also popularized the hierarchical file system with arbitrarily nested subdirectories, originally introduced by Multics. Other common operating systems of the era had ways to divide a storage device into multiple directories or sections, but they had a fixed number of levels, often only one level. Several major proprietary operating systems eventually added recursive subdirectory capabilities also patterned after Multics. DEC's RSX-11M's "group, user" hierarchy evolved into Virtual Memory System directories, CP/M's volumes evolved into MS-DOS 2.0+ subdirectories, and HP's Multi-Programming Executive group.account hierarchy and IBM's System Support Program and OS/400 library systems were folded into broader POSIX file systems.

Making the command interpreter an ordinary user-level program, with additional commands provided as separate programs, was another Multics innovation popularized by Unix. The Unix shell used the same language for interactive commands as for scripting (shell scripts — there was no separate job control language like IBM's Job Control Language). Since the shell and OS commands were "just another program", the user could choose (or even write) his own shell. New commands could be added without changing the shell itself. Unix's innovative command-line syntax for creating chains of producer-consumer processes (pipeline (Unix)) made a powerful programming paradigm (coroutines) widely available. Many later command-line interpreters have been inspired by the Unix shell.

A fundamental simplifying assumption of Unix was its focus on ASCII text for nearly all file formats. There were no "binary" editors in the original version of Unix — the entire system was configured using textual shell command scripts. The common denominator in the I/O system was the byte — unlike "record-based" file systems. The focus on text for representing nearly everything made Unix pipes especially useful, and encouraged the development of simple, general tools that could be easily combined to perform more complicated ad hoc tasks. The focus on text and bytes made the system far more scalable and portable than other systems. Over time, text-based applications have also proven popular in application areas, such as printing languages (PostScript), and at the application layer of the Internet Protocols, e.g. Telnet, FTP, SSH, SMTP, HTTP and SIP.

Unix popularized a syntax for regular expressions that found widespread use. The Unix programming interface became the basis for a widely implemented operating system interface standard (POSIX, see above).

The C (programming language) soon spread beyond Unix, and is now ubiquitous in systems and applications programming.

Early Unix developers were important in bringing the theory of Modularity (programming) and reusability into software engineering practice, spawning a "Software Tools" movement.

Unix provided the TCP/IP networking protocol on relatively inexpensive computers, which contributed to the Internet explosion of world-wide real-time connectivity, and which formed the basis for implementations on many other platforms. (This also exposed numerous security holes in the networking implementations.)

The Unix policy of extensive on-line documentation and (for many years) ready access to all system source code raised programmer expectations, and contributed to the 1983 launch of the free software movement.

Over time, the leading developers of Unix (and programs that ran on it) evolved a set of cultural norms for developing software, norms which became as important and influential as the technology of Unix itself; this has been termed the Unix philosophy.

2038 Unix stores system time values as the number of seconds from midnight January 1 1970 (the "Unix Epoch") in variables of type time_t, historically defined as "signed 32-bit integer". On January 19 2038, the current time will roll over from a zero followed by 31 ones (01111111111111111111111111111111) to a one followed by 31 zeros (10000000000000000000000000000000), which will reset time to the year 1901 or 1970, depending on implementation, because that toggles the sign bit. As many applications use OS library routines for date calculations, the impact of this could be felt much earlier than 2038; for instance, 30-year mortgages may be calculated incorrectly beginning in the year 2008.

Since times before 1970 are rarely represented in Unix time, one possible solution that is compatible with existing binary formats would be to redefine time_t as "unsigned 32-bit integer". However, such a kludge merely postpones the problem to February 72106, and could introduce bugs in software that compares differences between two sets of time.

Some Unix versions have already addressed this. For example, in Solaris on 64-bit systems, time_t is 64 bits long, meaning that the OS itself and 64-bit applications will correctly handle dates for some 292 billion years (several times greater than the age of the universe). Existing 32-bit applications using a 32-bit time_t continue to work on 64-bit Solaris systems but are still prone to the 2038 problem.

Free Unix-like operating systems

In 1983, Richard Stallman announced the GNU project, an ambitious effort to create a free software Unix-like system; "free" in that everyone who received a copy would be free to use, study, modify, and redistribute it. GNU's goal was achieved in 1992. Its own kernel development project, GNU Hurd, had not produced a working kernel, but a compatible kernel called Linux kernel was released as free software in 1992 under the GNU General Public License. The combination of the two is frequently referred to simply as "Linux", although the Free Software Foundation and some Linux distributions, such as Debian, use GNU/Linux naming controversy.

In addition to their use in the Linux operating system, many GNU packages — such as the GNU Compiler Collection (and the rest of the GNU toolchain), the glibc and the Coreutils — have gone on to play central roles in other free Unix systems as well.

Linux distributions, comprising Linux and large collections of compatible software have become popular both with hobbyists and in business. Popular distributions include Red Hat Enterprise Linux, Fedora (Linux distribution), SUSE Linux, SUSE Linux, Debian, Ubuntu (Linux distribution), Mandriva Linux, Slackware Linux and Gentoo Linux.

A free derivative of BSD Unix, 386BSD, was also released in 1992 and led to the NetBSD and FreeBSD projects. With the 1994 settlement of a lawsuit that UNIX Systems Laboratories brought against the University of California and Berkeley Software Design Inc. (USL v. BSDi), it was clarified that Berkeley had the right to distribute BSD Unix — for free, if it so desired. Since then, BSD Unix has been developed in several different directions, including the OpenBSD and DragonFly BSD variants.

Linux and the BSD kin are now rapidly occupying the market traditionally occupied by proprietary Unix operating systems, as well as expanding into new markets such as the consumer desktop and mobile and embedded devices. A measure of this success may be seen when Apple Computer incorporated BSD into its Macintosh operating system by way of NEXTSTEP. Due to the modularity of the Unix design, sharing bits and pieces is relatively common; consequently, most or all Unix and Unix-like systems include at least some BSD code, and modern BSDs also typically include some GNU utilities in their distribution, so Apple's combination of parts from NeXT and FreeBSD with Mach and some GNU utilities has precedent.

In 2005, Sun Microsystems released the bulk of the source code to the Solaris operating system, a System V variant, under the name OpenSolaris, making it the first actively developed commercial Unix system to be open sourced (several years earlier, Caldera had released many of the older Unix systems under an educational and later BSD license). As a result, a great deal of formerly proprietary AT&T/USL code is now freely available.

Branding In October 1993, Novell, the company that owned the rights to the Unix System V source at the time, transferred the trademarks of Unix to the X/Open Company (now The Open Group),http://groups.google.com/group/comp.std.unix/msg/c9974cf0022884f8 and in 1995 sold the related business operations to Santa Cruz Operation.http://www.novell.com/news/press/archive/1995/09/pr95220.html Whether Novell also sold the copyrights to the actual software was the subject of a 2006 federal lawsuit, SCO v. Novell, which Novell won; the case is being appealed. Unix vendor SCO Group accused Novell of slander of title.

The present owner of the trademark UNIX® is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX®" (others are called "Unix system-like" or "Unix-like"). The term UNIX is not an acronym, but follows the early convention of naming computer systems in capital letters, such as ENIAC and MISTIC.

By decree of The Open Group, the term "UNIX®" refers more to a class of operating systems than to a specific implementation of an operating system; those operating systems which meet The Open Group's Single UNIX Specification should be able to bear the UNIX 98 or UNIX 03 trademarks today, after the operating system's vendor pays a fee to The Open Group. Systems licensed to use the UNIX® trademark include IBM AIX (operating system), HP-UX, IRIX, Solaris (operating system), Tru64 (formerly "Digital UNIX"), A/UX, Mac OS X 10.5 on Intel Corporation platforms, and a part of z/OS.

Sometimes a representation like "Un*x", "*NIX", or "*N?X" is used to indicate all operating systems similar to Unix. This comes from the use of the "*" and "?" characters as "wildcard" characters in many utilities. This notation is also used to describe other Unix-like systems, e.g. Linux, FreeBSD, etc., that have not met the requirements for UNIX® branding from the Open Group.

The Open Group requests that "UNIX®" is always used as an adjective followed by a generic term such as "system" to help avoid the creation of a genericized trademark.

The term "Unix" is also used, and in fact was the original capitalization, but the name UNIX stuck because, in the words of Dennis Ritchie "when presenting the original Unix paper to the third Operating Systems Symposium of the American Association for Computing Machinery, we had just acquired a new typesetter and were intoxicated by being able to produce small caps" (quoted from the Jargon File, version 4.3.3, 20 September 2002). Additionally, it should be noted that many of the operating system's predecessors and contemporaries used all-uppercase lettering, because many computer terminals of the time could not produce lower-case letters, so many people wrote the name in upper case due to force of habit.

Several plural forms of Unix are used to refer to multiple brands of Unix and Unix-like systems. Most common is the conventional "Unixes", but the hacker culture which created Unix has a penchant for playful use of language, and "Unices" (treating Unix as Latin noun of the Latin declension#Third declension .28i.29) is also popular. The Anglo-Saxon language plural form "Unixen" is not common, although occasionally seen. Trademark names can be registered by different entities in different countries and trademark laws in some countries allow the same trademark name to be controlled by two different entities if each entity uses the trademark in easily distinguishable categories. The result is that Unix has been used as a brand name for various products including book shelves, ink pens, bottled glue, diapers, hair driers and food containers. .

Common Unix commands Widely used Unix commands include:



References

External links



UNIX / Linux Tutorial for Beginners
New users tutorial, with information on installing and compiling software packages.

UNIX Tutorial - Introduction
UNIX Introduction What is UNIX? UNIX is an operating system which was first developed in the 1960s, and has been under constant development ever since.

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The Open Group holds the UNIX trademark in trust for the industry, and manages the UNIX trademark licensing program.

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Unix < operating system > /yoo'niks/ (Or "UNIX", in the authors' words, "A weak pun on Multics") Plural "Unices". An interactive time-sharing operating system invented in 1969 by ...

Unix International from FOLDOC
Unix International < body > (UI) A consortium including Sun, AT&T and others formed to promote an open environment based on Unix System V, including the Open Look windowing system.

Home :: Unix@CMS :: University of Greenwich
Welcome to the CMS Unix website. On the following pages you will find information regarding the services and facilities provided by the University of Greenwich's CMS Unix Team as ...

UNIXhelp for users
Helpful information for users of the UNIX operating system, developed at the University of Edinburgh from work funded by the ITTI. Please read this disclaimer.

Unix - Wikipedia, the free encyclopedia
Unix (officially trademarked as UNIX, sometimes also written as Unix with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at ...

The UNIX and Linux Forums - the Top UNIX & Linux Q&A on the Web
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